Lennox pulse 21 furnace - nothing runs on but control board tries

I have a lennox pulse 21 furnace. Not sure when it was installed as it came with the house when I bought it. This winter the furnace began failing at random times and resetting the power fixed the problem. I've read some of the other posts here about the furnace but haven't found anything quite like this yet. i changed the main filter and did some basic cleaning etc.

After awhile, the problem became too frequent to ignore so I started to look into things. At first I thought the inducer blower motor was bad because this was the first thing to kick on when the power was turned on to the furnace. If the blower ran, then the furnace ran. If not, then not - but the control board still tried to activate the next thing in line after 15 seconds or so. So I found a new inducer motor pretty cheap and replaced it, and for a week or so it worked okay. But then the next thing in line after the inducer failed to kick on a few times. Now I'm at the point where the control board still 'clicks' as it tries to make things turn on but the inducer won't even work. So I'm thinking it's either a power issue or the control board but not sure where to go with it. I took the cover off of the control board, and found a few of the diodes weren't straight, they had bent over to touch other things and had stuck together a little. But without much electrical skill it's hard to diagnose the condition of the board.

I realize that replacement is recommended alot of times regarding this furnace, and I would love to but money is most definitely an issue right now so if there's a sulotion I can handle myself, I'd like to go that route first.

You will need to verify voltage from the board to the inducer. If you have the installtion manual there is a flow chart for the sequence of operation of the furnace.
The basic sequence is:
1. thermostat calls for heat
2. inducer motor starts and runs for a pre-set amount of time
3. the pressure switch closes and allows for ignition trial
4. ignition is proved back to the board allowing the system to operate.

Verify 120VAC to the inducer motor upon call for heat from stat, if you have 120 at the leads that connect to the inducer and it does not start , the motor is faulty. If the inducer starts use a voltmeter across the pressure switch terminals, a voltage reading of 0 VAC will verify contact closure and ignition should occur.

The pulse furnace was under a factory recall due to breaches in the heat exchanger, unfortunately for you, the Lennox Corp. has ended the program that allowed for an allowance / furnace for replacement. To test the heat exchanger a special kit is required from lennox that will verify integrity of the heat exchanger. (If the heat exchanger seal has been comrimised the pressure switch will not prove and the igniton sequence will be interupted and cause the system to go into "lock-out" mode).I know this is probably not what you wanted to hear. Hope this helps, please list as "very helpful" if it did

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The bearings are bad. You need to replace the motor. Motor cost $75 to $125. Labor is on avg. $150 to $400 with an decent A/C Company . You can try to oil it but its not recommend by Lennox. That furnace at the time they build it was top of the line. Good Luck.

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They don't. And why would you want to trade it out??? You are currently running off the communicating terminals. If you are going to install a nest you will have to match the nest wiring with the legacy/24volt terminals on the furnace control board and likely the outdoor unit will need rewired as well. Not extremely difficult but why??? The nest is not what it's cracked up to be!!

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MAYBE the module. If you call for help be sure they know how to work on a Pulse or they're likely to just tell you to replace the furnace (try to find a company that was a Lennox dealer at least 10 years ago). The Pulse is a very different animal that many in my industry don't understand and are quick to fault - the Edsel of the heating industry.

The bearings are bad. You need to replace the motor. Motor cost $75 to $125. Labor is on avg. $150 to $400 with an decent A/C Company . You can try to oil it but its not recommend by Lennox. That furnace at the time they build it was top of the line. Good Luck.

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